Multi-layer X-ray detector and X-ray system

Abstract

For particularly flexible application with regard to dual energy, a multi-layer X-ray detector is provided, comprising at least a first and a second sensor layer, which sensor layers are arranged one behind the other in the X-ray projection direction, wherein the first sensor layer is configured to convert X-ray quanta of a first emission spectrum into first signals and the second sensor layer is configured to convert X-ray quanta of a second emission spectrum into second signals, an intermediate space arranged between the two sensor layers, and at least one bendable layer band which has at least two filter areas with different material composition and / or coating, as well as a transport mechanism by which either a first filter area or a second filter area can be brought into the intermediate space.

Description

[0001] The invention relates to a multi-layer X-ray detector according to claim 1 and an X-ray system with a multi-layer X-ray detector according to claim 12.

[0002] Modern X-ray technology uses dual-energy X-ray tubes, i.e., X-ray tubes that can emit two different emission spectra. One of the emission spectra is generally high-energy, the other lower-energy. A significant energy difference between the two sensor layers is particularly important. From the two different X-ray images created in this way, the proportion of soft tissue can be subtracted, for example, and bone density can be measured. The material composition of the entire body tissue can also be calculated.

[0003] In addition to the dual energy X-ray tubes, dual energy X-ray detectors are also required to read the corresponding signals. One such well-known dual energy X-ray detector 9 - see Fig. 1 - generally has two scintillator-based sensor layers, which are arranged one behind the other in the X-ray projection direction 13. During the acquisition, an X-ray beam first penetrates the first sensor layer 10 and then the second sensor layer 11 along the projection direction 13. To achieve sufficient spectral separation for dual-energy acquisitions, a filter layer is typically present between the two sensor layers (e.g., a 1 mm thick copper filter layer 12). Such multilayer X-ray detectors are known, for example, from Ståhl, Fredrik et al., "Performance characterization of a prototype dual-layer cone-beam computed tomography system", Medical Physics Vol. 48, 11 (2021), pages 6740-6754.

[0004] A disadvantage of multilayer X-ray detectors is that the high absorption of the filter layer leads to a reduced quantum efficiency of X-ray detection.

[0005] US 2021 / 0 255 340 A1 discloses a multilayer X-ray detector with a fixed filter. US 4,859,849 A discloses another multilayer X-ray detector with a movable filter.

[0006] It is an object of the present invention to provide a multi-layer X-ray detector which, in addition to the sufficient spectral separation of X-ray images by means of a dual energy X-ray source, enables an improved quantum efficiency of X-ray detection.

[0007] The object is achieved according to the invention by a multi-layer X-ray detector according to claim 1 and an X-ray system with a multi-layer X-ray detector according to claim 12. Advantageous embodiments of the invention are the subject of the associated subclaims.

[0008] The multi-layer X-ray detector according to the invention comprises at least a first and a second sensor layer, which sensor layers are arranged one behind the other in the X-ray projection direction, wherein the first sensor layer is designed to convert X-ray quanta of a first spectrum (e.g. X-ray emission spectrum) into first signals and the second sensor layer is designed to convert X-ray quanta of a second spectrum (e.g. X-ray emission spectrum) into second signals, an intermediate space arranged between the two sensor layers, and at least one bendable layer strip which has at least two filter regions with different material compositions and / or coatings, as well as a transport mechanism by means of which either a first filter region or a second filter region can be brought into the intermediate space.

[0009] The layered strip is particularly flexible and can be bent, folded, or rolled without damaging the layered strip itself or any coatings. The filter regions can be large-area; in particular, they have an area that approximately corresponds to the area of ​​the second sensor layer, so that the entire intermediate space can be covered by one of the filter regions if necessary. The layered strip itself preferably has a total area of ​​at least twice the area of ​​the second sensor layer (at least two filter regions), but can also be significantly larger (e.g., neutral regions between the filter regions or even three or more filter regions). The layered strip is preferably arranged such that, in the region of the intermediate space, the surface normal of the layered strip is parallel to the X-ray projection direction.

[0010] The transport mechanism allows either the first filter area or the second filter area, with its respective material composition and thus filter effect, to be moved into the space between the two sensor layers as needed. This allows the user to select the filtration required for the current application and adjust it quickly and easily. Even during an ongoing procedure, rapid switching between the two filter areas is possible, for example, within a few seconds. The X-ray detector offers a high degree of flexibility with regard to the spectral separation of the at least two spectra with respect to the X-ray images. The filter areas have the most homogeneous composition and filter effect possible.

[0011] The use of such layer bands also ensures a high reliability of the filter effect, and the risk of artifacts in the resulting X-ray images is low.

[0012] According to one embodiment of the invention, the laminated band comprises a first spectral filter material with a first X-ray transmittance in the first filter region and a second spectral filter material with a second X-ray transmittance in the second filter region, with the first and second X-ray transmittances differing. The different X-ray transmittances also allow for a correspondingly different filter effect to be selected as needed.

[0013] In particular, the first X-ray transmittance is less than 25%, based on an X-ray photon energy of 50 keV, so that the first filter region exerts a spectrally particularly effective X-ray absorption. In this way, when the first filter region is positioned in the intermediate space, a particularly good spectral separation of the emission spectra and thus a particularly good dual energy resolution can be achieved, thus enabling a precise analysis of the material composition of the object under investigation. For such a purpose, the first filter material can contain or consist of at least one of the elements copper, tantalum, lead, aluminum, tin, brass or iron. For example, the first filter region can be sufficiently thick so that it absorbs low-energy (e.g., 40-80 keV) photons sufficiently well while simultaneously ensuring the lowest possible absorption of high-energy photons (e.g.,100-120 keV), so that enough still reaches the second sensor layer for reasons of detection and dose efficiency.

[0014] Advantageously, for a particularly large difference between the filter areas, the second X-ray transmittance is above 60%, in particular above 90%, based on an X-ray photon energy of 50 keV, so that the second filter area exerts only a weak or no X-ray absorbing effect. If the second filter area is positioned in the intermediate space, a particularly good quantum efficiency can be achieved for X-ray images. An X-ray detector that has a first filter area with low X-ray transmittance and a second filter area with high X-ray transmittance can therefore, depending on the conveyor belt settings, ensure good spectral separation in dual-energy operation and high quantum efficiency during normal operation, making it suitable and usable for a variety of applications with equally high quality.

[0015] According to a further embodiment of the invention, the layered belt is designed to be wound and / or unwound. For this purpose, the transport mechanism can, for example, comprise rollers onto which the layered belt is wound and unwound. Additionally, one or more motors can also be provided, which, for example, rotate the rollers and thus move the layered belt. For example, a roller can be provided on each side of the sensor layers outside the gap, and unwinding the conveyor belt on one roller and simultaneously winding it on the other roller can bring the respective filter area into the gap.

[0016] According to a further embodiment of the invention, the transport mechanism has rollers over which the layered belt is designed to be movable such that either the first filter area or the second filter area is transported into the intermediate space. In particular, the layered belt and the transport mechanism are designed as a conveyor belt, in particular as a motorized conveyor belt. In this form, the layered belt can be designed as a continuous, endless conveyor belt stretched over two rollers, for example, which is partially arranged in the intermediate space, with the two filter areas being arranged on different sides of the rollers. The motor drive causes the two rollers to rotate and move the conveyor belt so that, depending on the position, one of the filter areas can be positioned in the intermediate space.

[0017] According to a further embodiment of the invention, the first sensor layer comprises a first scintillator material of a first thickness and a first readout circuit, which first readout circuit is designed to detect photons generated by the first scintillator material from X-ray quanta of the first spectrum and to generate first signals therefrom. The second sensor layer comprises a second scintillator material of a second thickness and a second readout circuit, which second readout circuit is designed to detect photons generated by the second scintillator material from X-ray quanta of the second spectrum and to generate second signals therefrom. The functioning of sensor layers of X-ray detectors is generally known.

[0018] According to a further embodiment of the invention, the multilayer X-ray detector comprises a second, flexible layered band, which has at least two filter regions with different material compositions and / or coatings, as well as a transport mechanism by which either a first filter region or a second filter region can be brought into the intermediate space. Two or more layered bands can produce a multitude of different filter effects, depending on which filter regions are simultaneously positioned in the intermediate space. Such an X-ray detector offers a multitude of possibilities and variations ranging from strong spectral separation to very high quantum efficiency.

[0019] According to a further embodiment of the invention, the multilayer X-ray detector is designed either as a flat X-ray detector or as a fan detector. In a flat X-ray detector for cone-beam X-ray sources, the sensor surfaces are generally flat and comparatively large, for example, [20x30 cm or 30x40 cm], and consequently, the conveyor belt and filter areas are also correspondingly large. A fan detector for CT applications is generally curved in the shape of a circular segment, e.g., long but narrow. The conveyor belt and filter areas are also curved accordingly.

[0020] The invention also comprises an X-ray system comprising a multi-layer X-ray detector according to one of the preceding claims, comprising a dual energy X-ray source which is switchable from emitting the first emission spectrum to emitting the second emission spectrum and vice versa, and comprising a system controller for controlling the multi-layer X-ray detector and the dual energy X-ray source.

[0021] The invention and further advantageous embodiments according to the features of the dependent claims are explained in more detail below with reference to schematically illustrated embodiments in the drawings, without thereby limiting the invention to these embodiments. They show: Fig. 1 is a sectional view of a prior art multilayer X-ray detector; Fig. 2 a sectional view of a multilayer X-ray detector according to the invention with a layer band with two filter areas in a first state; Fig. 3 a sectional view of a multilayer X-ray detector according to the invention with a layer band with two filter areas in a second state; Fig. 4 a sectional view of another multi-layer X-ray detector according to the invention with a layer band with two filter areas in a first state; Fig. 5 is a sectional view of a multilayer X-ray detector according to the invention with two layer bands; Fig. 6 is a sectional view of another multilayer X-ray detector according to the invention with two layer bands; and Fig. 7 an X-ray system with a multi-layer X-ray detector and a dual energy X-ray source.

[0022] In the Fig. Figure 1 shows—as already described—a known dual-energy X-ray detector 9, in which a permanently installed, highly X-ray-absorbing filter layer is present between a first scintillator-based sensor layer 10 and a second scintillator-based sensor layer 11 in order to achieve sufficient spectral separation for dual-energy images. However, sufficient quantum efficiency is not possible with such a dual-energy X-ray detector 9 during normal operation.

[0023] In the Fig. Figures 2 to 6 show multilayer X-ray detectors 19 with layered bands 15, in which filter regions of a flexible layered band 15 can be transported by various transport mechanisms into a gap 14 between the first sensor layer 10 and the second sensor layer 11. Depending on the coating or composition of the filter regions, various filters can be created that achieve different effects, e.g., by either providing spectral separation in dual-energy operation or achieving sufficient quantum efficiency in normal operation.

[0024] In the Fig. 2 and Fig. 3 shows a multilayer X-ray detector 19 with a first scintillator-based sensor layer 10 and a second scintillator-based sensor layer 11, which sensor layers 10; 11 are arranged one behind the other in the X-ray projection direction 13. Between the two sensor layers 10; 11 there is a gap 14, e.g., over the entire length and width of the sensor layers. The multilayer X-ray detector 19 also has a layered belt 15 designed as a flexible, rollable, "endless" conveyor belt, which is stretched over, e.g., two rollers 18, wherein the rollers 18 are arranged on both sides of the sensor layers 10; 11, in particular of the second sensor layer 11. The rollers 18 are preferably arranged outside the angle of incidence of the X-ray radiation.The conveyor belt is located at least partially in the intermediate space 14 between the two sensor layers 10; 11 and extends at least partially, in particular completely, over the length and width of the sensor layers 10; 11. By a rotation 23 of the rollers, the conveyor belt is rolled over the rollers 18 and thereby changed in its position.

[0025] The conveyor belt has at least two filter areas, which, for example, have different spectral filter materials (different composition, thickness, density, etc.) with different X-ray transmittance. For example, a first filter area 16 can have a first filter material with low X-ray transmittance, and a second filter area 17 can have a second filter material with high X-ray transmittance. The filter materials can be applied to the conveyor belt, for example, as a coating. The layered belt 15 designed as a conveyor belt can be in the form of a film. The conveyor belt itself can also have a different material composition and / or a different thickness and / or density in the corresponding filter areas.

[0026] The first filter region 16 can, for example, have a coating containing one or more of the materials copper, tantalum, lead, aluminum, brass, tin or iron or can be at least partially formed from these. The coating is, for example, thick enough to exert a significant filtering effect (e.g., 1 mm copper). The second filter region 17 can have only a very thin coating of a material with high X-ray transparency, or no coating at all (e.g., only the layered tape / film) and thus an X-ray transparency close to 100%. Alternatively, the first filter region can have a thick coating and the second filter region a thin coating of the same material.

[0027] The sensor layers 10; 11 are constructed as in known multilayer X-ray detectors. Thus, the first sensor layer 10 can comprise a first scintillator material of a first thickness and a first readout circuit, and the second sensor layer 11 can comprise a second scintillator material of a second thickness and a second readout circuit. The respective readout circuits are designed to detect photons generated by the first scintillator material from X-ray quanta of the respective associated emission spectrum and to generate signals therefrom, which in turn are used to create X-ray images.

[0028] Depending on requirements, either the first filter area 16 or the second filter area 17 can now be moved into the intermediate space 14 by rotating the rollers 18, e.g., motor-driven, in the same direction of rotation 23. For this purpose, the rollers can be provided with drives (not shown). If the first filter area 16 with the low X-ray permeability is located in the intermediate space 14 - shown in Fig. 2 - and extends over the entire sensor surface of the second sensor layer 11, irradiation by a dual energy X-ray source with different emission spectra results in spectral filtering, by which tissue compositions can be determined from the resulting X-ray images (e.g., by subtraction). If the second filter area 17 with the high X-ray transparency is located in the intermediate space 14 - shown in Fig. 3 - this allows a composite X-ray image with high quantum efficiency to be created from the two X-ray images.

[0029] The transport mechanism can also - as in Fig. 4 - be designed such that two rollers 18 are arranged rotatably on both sides of the second sensor layer 11 outside the intermediate space 14 and the layered strip 15 is rolled up onto the other roll 18 by unrolling from one roller 18. This is done, for example, by motor-driven rotation of the two rollers 18 in the same direction of rotation 23. In this way, too, a filter area 16; 17 can be positioned between the rollers 18 such that it is located completely in the intermediate space 14 and extends, for example, over the second sensor surface 11. In order to ensure uniform filtration, the layered strip 15 has a (e.g. predefined) tension between the rollers 18. In order to maintain such tension, a spring mechanism can be provided, for example, in one of the rollers 18 or both rollers 18.

[0030] In the Fig. 5 and Fig. Figure 6 shows further embodiments of multi-layer X-ray detectors 19, each of which has two transport mechanisms with layered belts whose filter regions can be arranged one behind the other in the X-ray projection direction 13 in the intermediate space 14. This allows for additional filtering options.

[0031] In the Fig. 5, for example, two layered belts are present: a first layered belt 15.1 designed as an endless conveyor belt, which is stretched over two rollers 18 and has a first filter area 16 and a second filter area 17; and a second layered belt 15.2 designed as an endless conveyor belt, which is also stretched over two rollers 18 and has a third filter area 16.2 and a fourth filter area 17.2. The first layered belt 15.1 is arranged, for example, within the second layered belt 15.2. The filter areas can be arranged superimposed within the intermediate space 14 in the X-ray projection direction 13 and combined as required. For example, the first filter area 16 of the first layered belt 15.1 can be combined with the third filter area 16.2 of the second layered belt 15.2 or alternatively with the fourth filter area 17.2 of the second conveyor belt 15.2. The superposition results in a cumulative filter effect.By combining and depending on the individual filters, up to four different filter variants are possible.

[0032] Here, too, each conveyor belt can have a filter zone with low X-ray permeability and a filter zone with high X-ray permeability. The conveyor belts can be made of film or belt, for example, and coated accordingly in the filter zones or assembled from different pieces. The materials of the filter zones can vary in composition, density, and thickness. The conveyor belts and their coatings are flexible and bendable and should not suffer any cracks or breaks during unwinding.

[0033] In the Fig. 6 shows two layer belts 15.1; 15.2 arranged one behind the other in the X-ray projection direction 13, each with two rollers 18, which each have a transport mechanism as in Fig. 4. Each of the two layered bands 15.1; 15.2 can be rolled up by unwinding from one roll 18 onto the other roll 18 with motor-driven rotation of both rollers 18 in the same rotation direction 23. This allows one of the filter areas for each layered band to be moved into the intermediate space 14 depending on the position. In this way, two filter areas, one filter area of ​​the first layered band 15.1 and one filter area of ​​the second layered band 15.2, can always be arranged one behind the other and thus superimposed in their X-ray absorption effect. With two filter areas per layered band, up to four different filter variants are possible.

[0034] Each layered belt can also have more than two, e.g., three or four, filter sections. The motor-driven rollers 18 can be controlled, for example, by a controller in terms of their movement to set a specific positioning of the filter sections.

[0035] In the Fig.7 shows an X-ray system with a multi-layer X-ray detector 19 and a dual energy X-ray source 21, which is controlled by a system controller 24. The multi-layer X-ray detector 19 and the dual energy X-ray source 21 can, for example, be fixedly arranged on a C-arm 22, wherein the C-arm is spatially adjustable (e.g., orbitally, rotationally, or translatorily). In this case, the dual energy X-ray source 21 can be designed to emit a cone beam, and the multi-layer X-ray detector 19 can be designed as an area detector. In an area detector, the sensor layers are also flat. The system controller can also be used to control the positioning of the filter areas by moving the motorized rollers 18, depending on, for example, the planned application.

[0036] A computed tomography X-ray system is also possible, which has a gantry in which the multi-layer X-ray detector 19 and the dual-energy X-ray source 21 are arranged. In such a case, the X-ray detector is designed as a line detector, and the sensor layers are curved.

[0037] The coating material of the filter areas can also be mixed with other materials that increase flexibility and / or elasticity to enable damage-free unrolling. The filter material can be applied to an elastic carrier material.

[0038] Regardless of the grammatical gender of a particular term, persons with male, female or other gender identities are included.

[0039] The invention can be briefly summarized as follows: For particularly flexible applicability with regard to dual energy, a multi-layer X-ray detector is provided, comprising at least a first and a second sensor layer, which sensor layers are arranged one behind the other in the X-ray projection direction, wherein the first sensor layer is designed to convert X-ray quanta of a first emission spectrum into first signals and the second sensor layer is designed to convert X-ray quanta of a second emission spectrum into second signals, an intermediate space arranged between the two sensor layers, and at least one bendable layer strip which has at least two filter regions with different material compositions and / or coatings, as well as a transport mechanism by means of which either a first filter region or a second filter region can be brought into the intermediate space.

Claims

[1] Multi-layer X-ray detector (19), comprising • at least one first sensor layer (10) and one second sensor layer (11), which sensor layers (10; 11) are arranged one behind the other in the X-ray projection direction (13), wherein the first sensor layer (10) is designed to convert X-ray quanta of a first spectrum into first signals and the second sensor layer (11) is designed to convert X-ray quanta of a second spectrum into second signals, • a gap (14) arranged between the two sensor layers (10; 11), and • at least one flexible layered band (15) which has at least two filter regions (16; 17) with different material compositions and / or coatings, and a transport mechanism by which either a first filter region (16) or a second filter region (17) can be brought into the intermediate space (14). [2] Multi-layer X-ray detector according to claim 1, wherein the layer band (15) has a first spectral filter material with a first X-ray transmittance in the first filter region (16) and a second spectral filter material with a second X-ray transmittance in the second filter region (17), wherein the first and the second X-ray absorption coefficients differ. [3] A multilayer X-ray detector according to claim 2, wherein the first X-ray transmittance is less than 25% based on a photon energy of 50 keV. [4] A multilayer X-ray detector according to claim 2 or 3, wherein the first filter material contains at least one of the elements copper, tantalum, lead, aluminum, tin, brass or iron. [5] Multilayer X-ray detector according to one of claims 2 to 4, wherein the second X-ray transmittance is greater than 60%, in particular greater than 90%, based on a photon energy of 50 keV. [6] Multi-layer X-ray detector according to one of the preceding claims, wherein the layered strip (15) is designed to be rollable and / or unrollable. [7] Multi-layer X-ray detector according to one of the preceding claims, wherein the transport mechanism comprises rollers (18) over which the layered belt (15) is designed to be movable in such a way that either the first filter region (16) or the second filter region (17) is transported into the intermediate space (14). [8] Multi-layer X-ray detector according to one of the preceding claims, wherein the layer belt (15) and the transport mechanism are designed as a conveyor belt, in particular as a motorized conveyor belt. [9] Multi-layer X-ray detector according to one of the preceding claims, wherein the first sensor layer (10) comprises a first scintillator material of a first thickness and a first readout circuit, which first readout circuit is designed to detect photons generated from X-ray quanta of the first spectrum by the first scintillator material and to generate first signals therefrom, and wherein the second sensor layer (11) comprises a second scintillator material of a second thickness and a second readout circuit, which second readout circuit is designed to detect photons generated from X-ray quanta of the second spectrum by the second scintillator material and to generate second signals therefrom. [10] Multi-layer X-ray detector according to one of the preceding claims, comprising a second flexible layered band (15.2) which has at least two filter regions (16.2; 17.2) with different material composition and / or coating, and a transport mechanism by which one of the filter regions (16.2; 17.2) of the second layered band (15.2) can be brought into the intermediate space (14). [11] Multi-layer X-ray detector according to one of the preceding claims, which is designed either as a flat X-ray detector or as a fan detector. [12] X-ray system, comprising a multi-layer X-ray detector (19) according to one of the preceding claims, comprising a dual energy X-ray source (21) which is designed to be switchable from emitting the first spectrum to emitting the second spectrum and vice versa, and comprising a system controller (24) for controlling the multi-layer X-ray detector (19) and the dual energy X-ray source (21).

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